In U.S. Pat. No. 4,270,729 granted June 2, 1981, a top operated tank car valve assembly is disclosed, including a rod extending downwardly from the top of the tank attached to the valve stem of a lading valve located in the bottom of the tank. The stem engages a horizontally extending threaded valve sleeve provided with a mounting flange which engages a cooperating mounting flange on a valve cage. Vertically extending fasteners engage the upper surface of the sleeve, and extend through the valve cage and engage threaded openings in a tank car bottom outlet mounting flange. The cage includes a valve seat for a valve closure formed on the internal surface of the valve cage. Circumferentially spaced openings are formed in the valve cage for lading flow out of the tank. Laterally spaced projections extend upwardly from the lading valve closure. A valve stem retainer includes a pair of formed retainer clamps which define a cavity or opening. The clamps engage the lower end of the valve stem with a sufficiently tight fit as to substantially reduce horizontal and angular movement of the stem relative to the valve closure. A valve guide depends from the valve closure a sufficiently short distance as to not extend below the tank mounting flange, and thereby a skid is not required in order to comply with AAR and DOT regulations concerning projections extending below the bottom surface of a railway tank car.
While the subassembly of the valve closure, valve stem and valve sleeve can be carried out outside the tank, this subassembly must be placed in the tank from the top. And the fasteners extending vertically within the tank and into the tank bottom which hold the sleeve in engagement with the cage and hold the cage in place within the tank must be installed and removed with the operator inside the tank.
It is unpleasant working within a railway tank car. Furthermore, working inside the tank constitutes a safety hazard.